My 3 Deco M5's are wired together via D-Link switch. The main AP is in router mode.

When setting things up (via connecting one at a time and doing some random power cycling), I can get each of the leaf AP's to talk to the main router M5 via Ethernet. ie.,

Internet --- MAIN M5 ---- ethernet --- ATTIC M5
                 |
                 +------- ethernet --- DOWNSTAIRS M5

I check the app every day. For a few days, this network map remains.

One day I look at the app, and all of a sudden I see:

Internet --- MAIN M5 ---- wifi --- ATTIC M5 --- ethernet --- DOWNSTAIRS M5

I can play around with rebooting, unplugging, plugging back in, etc. - and voilla - it goes back to using Ethernet backhaul everwhere. Then a few days later, bang, back to some other configuration (not always the 2nd one depicted above, but will always revert to one of them using wifi).

Any ideas? I've tried different switch ports, confirmed the Ethernet connection is live, etc.